Secondary air supply system and nozzle for underfeed stokers



Jan. 15, 1952 E. c. WEBB 2,582,808 SECONDARY AIR SUPPLY SYSTEM AND NOZZLE FOR UNDERFEED STOKERS Filed July 16, 1948 ERNEST C. WEBB fl TTUR NE Patented Jan. 15, 1952 SECONDARY AIR SUPPLY SYSTEM AND NOZZLE FOR UNDERFEED STOKERS' Ernest C. Webb, Bay Village, Ohio, assignor'to; Iron Fireman Manufacturing Company, Portland, Oreg.

Application July 16, 1948, Serial No. 38,970

4 Claims.

In burning coking coal with a small single retort underfeed stoker, as is commonly used in connection with a residential heating boiler or Warm air furnace, it has been the common ex perience that as the coal proceeds through the 5 coal passage through the retort and tu'yere block section of the stoker, the coal is warmed by conduction from the coal bed above and oozes tarry hydrocarbons to an extent that makes the coal particles adhere to each other. Under the pressure of the feed screw forcing the coal through this section of the stoker the coal tends to form into a column which becomes a more or less hard mass as the more volatile hydrocarbons are driven off and burned as the column progresses 18 upwardly into the burning zone of the fuel bed. Although this coke column will vary in size and shape it resists orderly burning by presenting a much smaller total surface area to the incoming combustion air than would the indi- 20 vidual small pieces of coal from which the column was formed. The result of the formation of these larger consolidations of coke in the fuel bed is to slow down the burning of the fuel until the fuel bed builds up to an undesirable height as or the fire may even go out.

It is the general object of this invention to provide an auxiliary air system comprising botha means and a method of operation which will limit the height to which the fuel bed may rise without mechanical interference and at the same time to provide overfire air which has two ameliorating actions when the difficulties of of the retort and tuyres; and second, direct air at a considerable velocity down on to fuel bed from above and thus burn off the columnar coke formations from above as they occur.

To accomplish this general object in a practical way the particular object of this invention is to provide a nozzle or auxiliary air conduit end arrangement which makes this type of operation feasible by preventing the destruction of the nozzle or conduit end, and by the design of the nozzle or auxiliary air conduit end arrangement v to determine or provide a method of operation of the auxiliary air system which will preclude the destruction of the equipment.

That these objects are accomplished by the equipment and method of operation'of the in- 2 vention will become apparent on reference to the following specifications as illustrated in the accompanying drawing in which:

Fig. l is a conventionalized drawing in vertical section of a fragment of a residential size heating boiler having installed therein the burning head of a residential size underfeed stoker including the auxiliary air equipment of this invention.

Fig. 2 is a plan view of the burning head of the stoker shown in Fig. 1, showing the location in plan of the auxiliary air equipment of this invention. v

Fig.3 is an elevation in partial section of the auxiliary air conduit terminal equipment of this invention.

Like numbers of reference refer to the same or similar parts throughout the several views.

Referring nowto the drawing, there is shown a fragmental section through the combustion chamber of a residential size heating boiler having a base I I on which is resting a boiler having an outer shell l2 and an inner shell 13 with the space between the shells filled with water [4. Within the base H and resting on a fire brick or other support 15 on a floor It is shown the windbox I! of an underfeed stoker of conventional design. It is understood that the driving motor, the electrical controls, the coal storage hopper, the speed reduction gearing, the air fan, and other parts of the stoker which are usually arranged exterior to the boiler are omitted from the drawings for the purpose of confining attention to the novel parts and arrangement of the invention. However, there is shown a stoker coal feed screw l8 which feeds coal through a conveyor housing I!) and through an elbow or retort 22 within the windbox l1 and from which the coal rises within the ring of tuy'ere blocks 20 to form a fuel bed the ideal upper limit of which is indicated by the broken line 2| of Fig. 1. v

The windbox I 1 having outer walls 23, top closure 24, bottom closure 25 and inner wall formed by curved retort or coal conveyor elbow 22, communicates through opening (not shown) in top closure 24 with hollow tuyere -blocks 20 and through an opening in outer wall 23 with air duct. The stoker fan mentioned above but not shown is understood to supply combustion air through air duct 28 to windbox I! from where the air is delivered to the underside of the fuel bed through tuyre blocks 20 having openings 21 therein as required.

Air for combustion is also supplied to the fuel bed from above by the auxiliary air system of this invention comprising a flanged air conduit elbow 28 secured to windbox outer wall 23 by cap screws 30 and communicating with windbox I! through opening 29 in outer wall 23. Auxiliary air, conduit 3| is secured to elbow 28 by flange bolts 32 and continues upwardly into a reverse bend 33 from which its discharge end 34 depends to discharge air downwardly and approximately axially of the upwardly forming fuel bed. It is understood that the location of opening 29 in any side 23 of windbox I1 is a matter of choice for the particular installation and that the horizontal offset of the axis of conduit end 34 from the vertical axis of the ring of tuyere blocks 20 is a matter :of choice to obtain best results for the particular design and arrangement of windbox, retort, tuyere blocks, etc.

Shown resting on top closure .2 of windbox H is hearth support plate 35 upon which'issupported the molded refractory ceramic hearth 38 formed as desired for best combustion results and to protectfrom thermal destruction the inner shell l3 of the holler or furnace as well as the flanged connection between conduit elbow 23 and air conduit 3|.

Formed on air conduit 31 near its outlet ,end 34 is downwardly diverging conical flange .on skirt 3] having slots 38 formed therein.

In axial alignment with air conduit .end.3.4 is

a second conduit or nozzle shown generally as 39 duit end 34. At its upper end nczzlejs has .a

downwardly diverging outer surface .42 and at its lower end a downwardly converging conical surface 4.3. Malleable lugs .44 formed on the upper edge of nozzle 39 are sized for insertion through slots 38 of skirt .-.3.! on conduit end 34. Formed on conduit end 34 and nozzle 39 are raised surfaces (not shown) .which in assembly coact to maintain tnozzle ,39 in co-raxial relation with conduit .end and to space nozzle 39 from skirt 3] to maintain an airdischarge opening between them. In assembly nozzle 39 is telescoped over conduit .end 3.4 with-lugs 44 inserted through slots 3.8 up ,to the limit allowed by the spacing surfaces and lugs 4.4 are bent by tapping their upper ends outward with a hammer to n ,nozzle .39 in position. I

With the stoker in operation part of the com,- bustion air enters the fuel bed from below through tuyeres 27 andpartof the air is discharged downwardly Onto the fuel bed through nozzle 39.

Should thecokingtendency of the cokebeing burned .be so extreme. that the fuel bed height or coke column continues to increase it may finally push against the lower outlet opening ,of nozzle :39 which will from there on break up :the coke column mechanically. But if this pressure of coke against thelcwer opening of nozzle 39 were allowed-to stop :the flow of air through conduit 3| the high temperature conditions in the combustion space and fuel bed would lead to the thermal destruction of the nozzle and air conduit.

However, in the auxiliary air system of this invention it is seen'that'this couldnot occur for under the condition .of stoppage of air flow through the lower opening of nozzle 39 the air would continue to ,flow from the :end of conduit =3 into the-interiQrofnQ ne .39 whereit wo ld 4 be reversed in direction and flow upwardly in the annular space between conduit end 34 and nozzle 39 and impinge against the lower side of skirt 3! when itwould again be reversed in direction and be discharged downwardly onto the fuel bed outside the nozzle. This continued flow of air will not only continue the combustion over 'the top of the fuel bed but will also continue to cool both the air conduit and the nozzle and prevent their destruction from overheating.

I have nodesire to claim any of the previous art but I .do desire to preserve for myself the critical features of the design and-method of operation of my auxiliary air system as herewith set forth.

I claim:

1. An auxiliary ,airsystem for us'ewith a stoker burning coking coal, comprising a source of air under pressure, a nozzle, an air supply pipe for conducting air from said source to said nozzle, and co-operating means formed on said pipe .and

said nozzle for attaching said nozzle to the outlet end of said pipe, said nozzle having a frusto-conical exterior surfaceconverging in .the direction of air flow from said pipe and an interior surface cylindrical .at its inlet end and frusto-conical at its outlet end, said nozzleinterior being of larger diameter over its cylindrical length than the outer diameter oflsaid v.pipe and .of smaller diameter at its outlet end than the interior diameter of said pipe, said vco-operating means including means for locating said nozzle both axially and longitudinally of said pipe whereby when said said nozzle is attached to said pipe said pipe is telescoped Within the cylindrical portion of said nozzle and spaced therefrom, said pipe having formed thereon a conical skirt axially spaced from and diverging in the direction of said nozzle whereby when air is flowing through said pipe and said nozzle the major'portion of the airwill be discharged from the vertex outlet .of said nozzle if said outlet is open but should said .outlet be clogged said air will be discharged from said pipe into the conical interior of said nozzle from Where it will flow in a reverse direction in the cylindrical interior of said nozzle but outside said pipe and on leaving said nozzle will impinge on said skirt and thereby be deflected to discharge in a hollow conical stream diverging in the directionof air flow .in said pipe.

2. In combination, a furnace, a source of air under pressure, a first conduit for conducting air from said source to theinterior of said furnace, at second conduit surrounding the discharge end of said first conduit andspaced therefrom, said second conduit extending beyond the end of said first conduit to form a nozzle therefore, a flange surrounding said first conduit and spaced from said second conduit, whereby should the outer end of said second conduit become clogged the said air will be conducted from the end of said first conduit to the spacebetween said conduits and ejected from said second conduit in a reverse direction against said flange thereby :again reversing the direction of said air to cause said 5 air to discharge approximately in its original direction of flow.

3. A pipe having a downwardly pointing vertical portion at one end and a downwardly diverging conical flange surrounding said vertical portion near said end, together with a nozzle member in axial alignment with said pipe at said end, said nozzle member being open at both ends and having an upper cylindrical part of larger diameter than said pipe and a lower portion converging to a smaller diameter than said pipe, said pipe end being telescoped into said nozzle for the cylindrical part of its length, and means for holding said nozzle in radial spaced relation to said pipe and in axially spaced relation to said flange.

4. An auxiliary air system for use with an underfeed stoker for burning coking coal, comprising a downwardly discharging secondary air pipe, a funnel shaped nozzle disposed under the lower end of said pipe and spaced around the tip thereof and a skirt spaced from the upper edge of said nozzle and surrounding said pipe, said skirt covering the space between said pipe and 6 nozzle whereby air passing downwardly from said pipe through said funnel shaped nozzle will entrain air beneath said skirt for the purpose of cooling said nozzle and raising the temperature of the secondary air issuing therefrom. ERNEST C. WEBB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS I Number Name Date 852,209 Watson Apr. 30, 1907 1,260,378 Hays Mar. 26, 1918 1,538,489 Potter May 19, 1925 1,602,845 Burhorn Oct. 12, 1926 FOREIGN PATENTS Number Country Date 17,179 Great Britain Aug. 9, 1898 457,577 Great Britain Dec. 1, 1936 58,425 Norway Sept. 27, 1937 72,045 Norway May 5, 1947 

